Automotive engineers have sought to provide systems that reduce the injuries that people sustain in a collision and that are very comfortable to the occupants within the automobile when the systems are not needed. Two systems devised by these engineers are (1) seatbelts having a pretensioner which activates during a collision, and (2) airbags.
A seatbelt with pretensioner allows free movement of the seatbelt while an occupant rides in the automobile. If the automobile is involved in an accident, the pretensioner system automatically tensions the seatbelt within the first few moments of the accident by igniting a combustible mixture that expands against a mechanical tensioning system for the belt. The occupant is held in place by the tightened seatbelt, and many injuries are avoided.
Airbags are also used to prevent and minimize injuries. Airbags are usually folded and neatly integrated within the automobile's interior when not needed to provide an aesthetically pleasing environment. However, if the car is involved in an accident, sensors within the airbag deployment system sense the deceleration force and direction and deploy the appropriate airbags within the automobile to restrain the occupant's movements and again prevent or minimize injuries. Airbags are usually deployed by igniting a combustible mixture within the first few moments of the accident and allowing the products of combustion to fill the airbag.
Automotive safety engineers are incorporating more airbags into automobiles in an effort to minimize injuries during a crash. Driver and front-seat passenger airbags are common in many automobiles and are mounted in the steering wheel and in the dash facing the passenger, respectively. Some automobile manufacturers are now also incorporating airbags into the doors of automobiles to restrain an occupant's movement toward the door and window glass during a collision, and it is likely that multiple airbags will be located throughout the car to protect both front- and rear-seat passengers during collisions. Airbags are also being introduced into passenger aircraft.
Seatbelt pretensioning systems and airbag deployment systems typically utilize a combustible composition to provide the motive force that tensions the seatbelt or that deploys the airbag. The composition combines with a source of oxygen when ignited and produces a large amount of gas to provide sufficient pressure to tension the seatbelt or to provide a sufficient volume of gas to deploy the airbag.
The amount of gas generated from the combustible composition increases substantially as more airbags and seatbelt pretensioners are added to vehicles. The gas is present within the vehicle's interior after the accident occurs, and an occupant rendered unconscious by the crash can inhale the gas for a long period of time before the occupant is extracted from the wrecked vehicle.
Propellants used in airbags or seatbelt pretensioning systems to date produce large amounts of noxious or toxic gases such as NO, NO.sub.2, carbon monoxide, SO.sub.x, HCl, NH.sub.3, or HF. Two common propellants used in these systems are nitrocellulose and BKNO.sub.3. Nitrocellulose is usually an unstable composition that degrades rapidly at the conditions present within an automobile's interior. Consequently, nitrocellulose for use in airbags or seatbelt pretensioners usually has substantial amounts of stabilizer added to it to prevent premature combustion in hot conditions. Nitrocellulose also produces large amounts of NO, NO.sub.2, and carbon monoxide to which a person is exposed when an airbag or seatbelt pretensioner activates. BKNO.sub.3 is a fairly stable material at the conditions present within an automobile's interior, but, when BKNO.sub.3 is ignited, it produces large amounts of NO and NO.sub.2. Thus, the amount of toxic gases to which an occupant of an automobile involved in a crash is exposed increases substantially as the number of airbags and seatbelt pretensioners within the vehicle increases.
It is therefore an object of this invention to provide combustible compositions that are suitable as propellants for, e.g., airbags or seatbelt pretensioners, or for other purposes.
It is an object of this invention in certain preferred embodiments to provide combustible compositions that are suitable as propellants for airbags or for seatbelt pretensioners and which produce little or no NO, NO.sub.2, carbon monoxide, SO.sub.x, HCl, NH.sub.3, and HF.
Further objects are apparent from the discussion herein.